In the past year membrane ATPase has been incorporated into a phospholipid model membrane. The voltage changes and the short circuit current changes appropriate to Na ion pumping have been observed upon adding ATP. These electrical phenomena are also obtained with acidic phospholipids alone, in which preparations molecular mechanism is apparent. The same mechanism is postulated for the enzyme. Further work will be done with membrane ATP-ase in model lipid membranes to try to test the hypothesis for the electrical changes, to try to approach the molecular mechanism of the actual pumping of Na ion, and to try to relate this enzyme to the previously described K ion selective channels in phospholipid membranes. A recent innovation appears to allow the assymetrical orientation of solubilized ATP-ase in a phospholipid membrane.